The present invention relates to percutaneous implant devices and in particular to pharmaceutically protected percutaneous implant devices.
A percutaneous device functions to maintain an opening in the skin through which either wires or pipes can pass from the outside world into the bodies of men or animals. Thus, percutaneous devices serve as lead throughs for either wires or pipes from the outside world into the bodies of men or animals.
The outside surface of a wire or pipe usually lacks compatibility with the living body tissues. Thus, a percutaneous device consists of a structure having an opening to receive the wire or pipe and an outside surface sufficiently compatible with the skin and the subcutaneous tissue to avoid rejection for a period of time useful to the patient. The percutaneous device interfaces with the body tissue and has an inner surface that provides a close, bacteria-tight junction with the outside surface of the wire or pipe that penetrates into the interior of the living body.
Movement of the percutaneous device causes irritation at the site where the device contacts the skin and the subcutaneous tissue. Such irritation contributes to early failure and rejection of the percutaneous implant. Thus, many percutaneous devices include a flange intended to be implanted subcutaneously to distribute mechanical forces over a larger area than the cross-section of the pipe or wire. This distribution of mechanical forces reduces the mechanical irritation that results at the junction of the living tissue and the percutaneous device.
When bacteria and other foreign bodies invade the junction between the skin and the implant, this too causes the failure or rejection of percutaneous devices.
Foreign material entering the junction where the gingival tissue surrounds a natural tooth can cause an inflammatory reaction. However, the gingival and subgingival region immediately adjacent to the surface of the tooth contain entities which stimulate an increased, localized, phagocyte activity as soon as any foreign material enters into the junction between the gingival tissue surrounding natural teeth and the tooth itself.
A solid solution of Gentamicin in methylmethacrylate has been used successfully in orthopaedic surgery, but has not found a use in connection with percutaneous implants prior to the present invention.
Polymethylmethacrylate, which is usually called bone cement or abbreviated PMMA, has been used to fix joint replacements, like artificial hip joints or knee joints, into the surrounding bony tissue adjacent to the joint. As the PMMA cures, it takes the antibiotic Gentamicin into solid solution. The temperature of PMMA reaches 100.degree. C. during the curing, and most other antibiotics do not survive this curing process because their molecular structures are too complicated. The Gentamicin diffuses out of the cured PMMA over very long periods of time, on the order of years, so that a local concentration of this antibiotic can be maintained without subjecting the whole body to this concentration. Moreover, the local concentration is sufficient to ensure that the bacteria will be destroyed in the immediate environment of the PMMA. This technique is widely used in particular in secondary joint replacement operations where the danger of infection is much higher than in primary operations. In such cases, the Gentamicin containing cement remains in situ for the lifetime of the implant and hopefully for the whole lifetime of the patient.
Infected bone wounds and infection in bony tissue provide other applications for PMMA infused with Gentamicin. In these cases, the general practice is to prefabricate PMMA into small spheres, each having a little stainless steel wire extending diametrically through it. These wires are connected to each other to form a chain. Such chains are inserted into infected areas in bony tissue, left there until the infection has ceased, and then removed in a second operation. Thus, when the Gentamicin diffusing from the spheres has eliminated the infection, the surgeon can remove the spheres by getting hold of a single sphere and just pulling out the entire chain of spheres.
FIG. 28 of Grosse-Siestrup et al, "Design Criteria for Percutaneous Devices," Journal of Biomedical Materials Research, Volume 18, pp. 357-82 (1982), illustrates a device for periodically treating the three-phase junction between the percutaneous device, the skin, and the outside air. It comprises an annular sleeve which is slipped over the lead-through and placed above the skin and intended to float in the three-phase junction. This annular sleeve provides a conduit for liquids, such as cleaning fluids or antibiotics, which are pumped through the sleeve via a squeeze bulb or the like, to clean the outside part of the skin adjacent to the percutaneous device. The device is then removed until the procedure is repeated. However, these devices to date have failed to extend the time between implantation and failure of the percutaneous device to any significantly appreciable extent. They also require the periodic attention of a human operator.
An infection control device that is related to vascular catheters is known by the brand name VITA CUFF and distributed by Baxter Health Care Corporation of McGaw Park, Illinois. The VITA CUFF device also surrounds a cylindrical catheter at a desired anatomical site and secures itself to the catheter by applying radial compression to the catheter. The VITA CUFF device has an outer tissue-interfacing surface that has a porous matrix consisting of a collagen sponge. Silver ions are bound to the collagen matrix to provide antimicrobial activity during the four to six weeks it takes for the collagen sponge to be completely absorbed by the surrounding tissue. Thus, this device likewise fails to extend the useful life of the implant for a period on the order of several months or years.